Kevin Israel writes:
Since MediaWiki 1.26, all ResourceLoader modules are loaded asynchronously, so inline scripts now need to account for the possibility they may be executed before the jquery and mediawiki modules have loaded.
If you use ResourceLoader::makeInlineScript() to build the HTML script element, your JavaScript code will be automatically wrapped in an anonymous function and queued for execution once ResourceLoader has started up.
Thank you! I have documented your advice at https://www.mediawiki.org/wiki/ResourceLoader/Migration_guide_%28users%29#In....
DanB